In this interview conducted at Pittcon 2023 in Philadelphia, Pennsylvania, we spoke to this year's recipient of The Chromatography Forum of the Delaware Valley Dal Nogare Award, Luis Colón.
Please could you introduce yourself and your current activities?
My name is Luis Colón, the A. Conger Goodyear Professor in the Department of Chemistry at the State University of New York at Buffalo. I am also a distinguished professor at the State University of New York at Buffalo and Associate Dean in the College for Arts and Sciences.
My research activities involve studying chromatographic and other materials for chemical analysis, and I have a research group of six students. Just two months ago, the 35th Ph.D. student graduated from my research group.
Revolutionizing Chemical Analysis: Discovering the Power of Capillary Electrophoresis
How did you become involved with the chromatography field?
My very first chromatographic experiment was in high school in a biology class where we did some paper chromatography. It was not until I went to college that I was exposed to HPLC and gas chromatography.
When I finished my bachelor's degree, I went to the pharmaceutical industry, where I became a practitioner of HPLC. After a five years, I went to graduate school, where I studied chromatographic detection systems for HPLC.
After that, I continued in the field of separations doing capillary electrophoresis during my postdoctoral research. Then, when I had my own research group, I continued to work in separation science, developing methodologies for analytical chemistry (i.e., chemical analysis) and developing materials for chromatographic separations by HPLC, electrochromatography, and gas chromatography.
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What are some challenges in analyzing complex molecules, such as pharmaceutical or environmental samples?
The challenges come and go, and then other challenges appear, making our life a little more interesting. I have found through the years that complex samples are difficult to separate—for example, there are matrix effects and/or multiple sample components.
Some of the samples like biofluids contain an enormous number of compounds that we need to separate or purify, which becomes very challenging.
One of the major challenges is to remove the unwanted matrixes. Some other challenges include identifying low-level impurities that are very difficult to detect, but we have been overcoming these challenges.
Nowadays, one other significant challenge is that we must do the analysis in a very short time and in many cases with relatively less funding. This is one challenge that many individuals in the field continue to face.
How would you define HPLC?
HPLC, high perfrormance liquid chromatography, is a separation technique in the liquid phase that uses a chromatographic column. This column is well-packed with a very small particulate material, an absorbent, that can interact with the compounds to be separate, and these are retained selectively depending on the compound and the composition of the material in the column.
You have a solution stream carrier (i.e., mobile phase) that brings the injected sample into the column. Then, the column is continuously washed with the carrier olution until the separated compounds are eluted out of the column and you can detect them as tehy elute from th column.
On the other hand, you have gas chromatography where the separation is carried out in the gas phase. This is that the mobile phase is a gas, which takes the sample into the column after sample volatilization and then pushes it through the column until the components are separated.
In gas chromatography, the mobile phase is a gas; in liquid chromatography (i.e., HPLC), it is a liquid; and in supercritical fluid chromatography, another separation technique, the mobile phase is a supercritical fluid. There are differences among the three of them. Gas chromatography is more amenable to volatile compounds. Liquid chromatography can handle compounds that are not volatile.
Supercritical fluid chromatography, on the other hand, is a technique with characteristics somewhere in between liquid chromatography and gas chromatography. This provides advantages because one can control some properties that facilitate further the separation of compounds.
The good thing about supercritical fluid chromatography is that it is more benign for the environment. CO2 collected in cylinders is used as the mobile phase to carry out the separations under supercritical conditions. We can modify it with some additives, like alcohols, but in general, CO2 is mostly used, and then it is returned to the environment in a much eco-friendlier process than using organic solvents like in HPLC. It can be seen as recycling the CO2. Supercritical fluid chromatography also provides us with fast separations and that is very advantageous.
Could you explain what photochromism is?
It is a process by which a particular molecule transforms, such as an isomerization, by light absorption. A photochromic molecule absorbs light and, in that process, changes its conformation and becomes something else, although of similar molecular structure. It now becomes a molecule that may have a color, for example, when before it did not have it.
A perfect example is the transition lenses we use for solar protection. If we are inside, we have a transparent colorless glass. If we go outside, the sun’s UV light hits the glass, and it changes color. This is due to the photochromic compound in these lenses, and that color now becomes a filter as well. UV light cannot penetrate and harm our eyes.
Why are the photochromic compounds, i.e., diarylethenes or DAE, with photo-switch for isomers, interesting materials for research applications?
These are unique compounds. These photochromic compounds go through back-and-forth transformations, like a switch, between two isomers. When certain light is present, these compounds convert to something slightly different (i.e., different isomeric compound), but if we take the light out or put a different color of light in, they convert back to the original compound.
Most of the present applications of these materials are in the liquid phase, meaning that these materials are in solution.
The Power of Separation Science to Prepare Chromatographic Materials - Luis Colón at Pittcon 2023
Video Credit: Pittcon
Diarylethenes tend to be relatively stable, as photo-switches, and can withstand many cycles of transformations, switching between the two conformational isomers. They do not necessarily need to be in the liquid phase or in a very specific matrix to switch colors (i.e., conformation).
Because of their characteristics, these compounds can be transformed to the solid phase and/or incorporated into solid devices. They can be in the crystal form and change conformation by shining light. Researchers making certain devices could incorporate crystalline diarylethene compounds to control devices by shining light.
It would be possible, for example, to manipulate the properties of a device to arrange it in a conformation that may allow transport of a molecular cargo to a specific site, which can then be released by exposure to a particular color of light.
Are there any challenges associated with isolating these compounds?
The compounds can go through the transitions when exposed to light when they are active; they have a particular photochemical state. These compounds also have rotamers (conformational isomers). You have this compound with little molecular arms that are always rotating, and one must have a particular conformation to convert from one form to another. However, this is not straightforward.
So, you shine UV light on one of these compounds in solution, giving a color change (conformation change). But a portion of the compound, or a set of compounds, does not change because it is in the wrong conformation. Therefore, you have a mixture when you do this in the liquid phase.
If you try to make a crystalline material with this mixture, for example, you do not know what you have initially in terms of their conformational state. The material can be ineffective in changing color or conformation when exposed to light because you did not have a pure material to start. Instead, you had a mixture. There is also something called fatigue, meaning that the diarylethene compound can switch between conformers for some time when exposed to light, and then it takes a different molecular conformation that does not change; i.e., it is not active anymore. There can be multiple isomeric compounds in the mixture.
The question is, how can you obtain each one of them? The main idea is to have a compound that is locked in place; this is you shine light so it takes a particular desired confirmation. Can you use that compound to make a material now that you have locked the molecule in place, and can you switch back and forth between the isomeric compounds?
It is not easy to separate/isolate them and make significant quantities to perform further studies. This is where we have been working in the field so that we can separate them, collect the sample that we are interested in, and then use that sample.
As they are isomers, it is particularly challenging to separate them, since they are very similar. You need the right conditions to separate them and collect the required quantities.
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Could you discuss some chromatography techniques that could be used to analyze these compounds?
Liquid chromatography can be used to separate these compounds quite easily. What people have not done in the past is use the sophistication of HPLC.
We use a detection system that allows us to perform spectroscopy. We collect the UV-visible spectrum as a means of characterization of the separated compounds on the fly; then, we can try to isolate them for chromatographic purposes. We can perform chromatography that instead of using a small column (analytical column), we use a large column (prep column), enabling us to collect large quantities. We have already performed this; it was the first isolation of relatively large quantities.
Isolation of large quantities requires a lot of solvents and that is not friendly to the environment. A small amount of acetonitrile can be used and disposed of easily when using small analytical columns. However, when it comes to a separations that takes 30 minutes using a large prep column with a flow rate of 20 milliliters per minute, meaning gallons of this solvent material are being produced as waste.
Therefore, we have switched to supercritical fluid chromatography because it does not use such a large quantity of solvent. This allows us to perform separation faster and be more environmentally friendly.
Are there any trends in chromatography and the broader separation sciences that you are currently monitoring or looking forward to seeing?
Chromatography, in general, is very useful for chemical analysis. The challenge of separating more complex samples is always there because we solve one problem, and another one comes along.
For example, compound separation in metabolomics requires more powerful separation techniques. I see a trend in using two-dimensional chromatography, where you can use two chromatographic techniques that are complementary (i.e., orthogonal) to each other to allow separation of complex mixtures.
Carrying out faster separations is also essential and will continue to advance in the future. There is another trend of trying to miniaturize the separation systems. Traditionally, at the analytical level, a column is used for the chromatography that runs the mobilephase at a milliliters per minute level.
We can do better by moving to capillary columns and reducing the flow rate. If we use supercritical fluid, we can also remove the solvent waste. I think there is going to be more emphasis on creating sustainable chromatographic methods. I think we know how to do it, but I do not think people had the motivation to do it. I believe we have become more conscientious about the environment, as well as cost savings, which is a trend I can foresee continuing.
Another trend is personalized medicine, where separation science can play a significant role, particularly using separation microdevices. I can envision having to go to the physician's office where they have one of these devices. You put a drop of blood in, its components are separated, and a system can detect such components, reflecting the health state of the individual.
How does it feel to win the Dal Nogare Award?
It gives me a sense of satisfaction because the work I do with my students and collaborators, carried out in my laboratory, has been recognized. I think that is a sense of accomplishment. There is also a sense that the work is essential and people have recognized its value.
I was talking to colleagues here at the meeting that we often do some things, and although they are exciting, we move forward and go to another project. It is not until five or ten years later that you realize that the work has been picked up and people are using some of the technology you developed. It may have been improved some what, but the principle is the same.
I think this award is a sense of satisfaction for me and my students because we feel we have contributed to the field in a significant way.
What are you looking forward to most about the next Pittcon in San Diego?
As I understand it, Pittcon will be on the West Coast for the first time. This is exciting because people could easily travel before, but traveling has become more restricted nowadays.
Expanding the meeting from the east coast of the United States to the west coast will allow scientists in that area, who may have not participated in the past, to now experience the meeting. It would be much easier for them. I look forward to sharing the science with the attending scientists and being in person again.
I like to build relationships, and it is easier when we are together in a meeting. Sometimes we finish a meeting and get together to go to dinner and have great discussions around science and other topics. Many scientists go there because of these discussions, in and out of the meeting, that can lead to new discoveries.
Why are these events so crucial to continue and for academics and industry professionals to encourage each other to attend them?
There was a big push before the pandemic to have classes online in academia. All these things were being pushed forward because it was thought that was the future of education and meetings.
It is not the same when you are in front of a computer screen. So, having these meetings in person is completely different. People may argue that science is the same. However, there is a human aspect to it, and I think you can only find that when you meet in person.
I do not think you can substitute the relationship building that takes place in in-person meetings with virtual meetings.
About Luis A. Colón Ph.D.
Luis A. Colón is an expert in analytical chemistry, with a focus on separation science. He can speak to the media about research advancements in this area. He can also discuss diversity in STEM, including recruitment, mentoring and support of students of color.
Colón’s lab focuses on developing techniques for separating chemicals in a mixture from one another, which is necessary in chemical analysis. His work has included the development of chromatographic media for chemical separations, detection schemes for monitoring mass-limited samples, and the development of strategies to separate and analyze complex chemical or biochemical sample mixtures, such as biofluids, protein digests and pharmaceutical drugs.
Colón has been widely recognized for his research and his successful efforts to increase diversity in STEM, particularly in the chemical sciences. He has helped recruit dozens of students to Buffalo from his native Puerto Rico to study or do summer research at his institution. As of 2023, over 20 had received advanced degrees in chemistry, mostly PhDs, from UB.
In 2015, Colón was named by President Barack Obama recipient of the Presidential Award for Excellence in Science, Mathematics and Engineering Mentoring — one of many awards Colón has received for his work to advance diversity and for his research.
This information has been sourced, reviewed and adapted from materials provided by Pittcon.
For more information on this source, please visit Pittcon.
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